The present invention relates to a system for more accurately controlling the delivery of flowable material to a patient. Particularly, the system may be used in the injection of hard tissue implant materials. Features of the invention provide for effective loading of an applicator configured to generate high fluid delivery pressures.
The introduction of flowable material to an implantation site within a patient to effect one or more therapeutic goals is well known. The flowable material itself may be of high or low viscosity. Matter ranging from typical fluids or solutions to non-Newtonian fluids, pastes, gels and the like has been used for one purpose or another in the medical arts.
It is well-recognized that syringes may be used for percutaneous delivery or injection of flowable material. However, such devices are of limited value in the delivery of high viscosity fluids. In general, users are only capable of generating pressures of about 100-150 psi with 10 cc syringes. This places a limitation on the viscosity of the flowable material that can be effectively xe2x80x9cpushed throughxe2x80x9d the syringe and attached needle or cannula and fully delivered to a treatment site. The use of a small barrel syringe, e.g., a 1 cc syringe enables the user to generate higher driving pressures (e.g., pressures of 800 psi and possibly as high as 1000-1200 psi) that may be used to flow a viscous implant material. However, the 1 cc volume of the syringe may be very limiting as to the amount of material deliverable to a patient. This can be especially problematic when the material to be injected is a settable composition where (for various reasons) it is important to deliver all the material desired in a single xe2x80x9cshotxe2x80x9d. Another problem with a 1 cc syringe is lack of control, as high pressures are generated in a xe2x80x9cspike-likexe2x80x9d response time and are not continuously controllable.
Other devices used in the medical arts do not suffer such a control problem by virtue of a threaded arrangement used to advance a piston head within a bore to drive material from a loaded device. U.S. Pat. No. 29,083 to Irving discloses a syringe having a plunger with a screw thread on its exterior. Advancing the plunger by turning it relative to a housing generates sufficient pressure to force a semi-solid ointment out of a perforated tube. This applicator, however, is only configured for rectal delivery of a hemorrhoid medicament.
By contrast, U.S. patent application Ser. No. 09/053,108, entitled xe2x80x9cPressure Applicator for Hard Tissue Implant Material,xe2x80x9d by Preissman, filed Apr. 1, 1998 and U.S. Pat. No. 6,383,190, entitled xe2x80x9cHigh Pressure Applicator,xe2x80x9d by Preissman, filed on even date herewith, each incorporated by reference herein as part of the invention, disclose high pressure applicators utilizing two threaded columns in various arrangements capable of use for injecting material in useful procedures.
While the applicator of the earlier-filed patent application by Preissman does not provide some of the advantages of the present invention (particularly in loading implant material), the applicators disclosed in each patent application are of practical utility as high-pressure applicators for use in percutaneous vertebroplasty. In this procedure, once a cannula is positioned in the cancellous bone of a vertebrae, a hard tissue implant material such as Polymethylmethacrylate (PMMA) is injected into a site for treatment to reinforce and solidify the damaged hard tissue.
Generally, about 3.5 cc of implant material per side of the vertebral body is required. Control issues aside, this makes the use of a 1 cc syringe problematic. Basically, a vertebroplasty procedure would require multiple reloading steps with such a syringe. Further, the additional time spent for such action would result in more than mere inefficiency. Reloading time is time spent while an implant material like PMMA is polymerizing to become increasingly viscous beyond a state in which it may be safely or effectively delivered by any type of injection device, regardless of its high-pressure capacity. Both the need to inject the implant material through a relatively narrow needle or cannula and the fact that the desired site is relatively closed (i.e., trabecular bone) compounds material thickening effects which make xe2x80x9csingle shotxe2x80x9d delivery ability important.
While PMMA in a nearly-solidified state is inappropriate for use with the present invention, a highly-viscous or syrupy consistency of PMMA is generally believed to be most advantageous for performing percutaneous vertebroplasty. Such a consistency insures that the implant material stays in place much better than a less viscous, more flowable material.
It is known that leakage or seepage of PMMA from a vertebral implant site or extravasation through fractures in the bone can cause a host of complicationsxe2x80x94some of which can be very serious and even result in death. For example, Weil et al. reported cases of sciatica and difficulty in swallowing which were related to focal cement leakage, Radiology 1996; Vol. 199, No. 1, 241-247. A leak toward the distal veins poses an even more serious risk, since this can cause a pulmonary embolism which is often fatal.
In addition to leakage around the cannula and through bone, overfilling of the intended implant site can result in introduction of implant material into the blood stream after removal of the cannula from the implant site. Due to the high pressures involved in the implant procedure, compliance within the delivery system can act as a capacitance under pressure thereby storing a volume of the implant material and energy under pressure which, upon release of the pressure, drives an undesired additional amount of implant material into the implant site to cause potentially-dangerous overfilling. This additional amount of outflow is sometimes referred to as xe2x80x9coozingxe2x80x9d or xe2x80x9cdripxe2x80x9d. System compliance may also result in decreased response performance of the delivery system.
Compliance may be introduced into a system either by virtue of appreciable elasticity of tubing, by other members forming part of the delivery system or by air bubbles introduced in the filling or loading of the applicator with implant material. Purging of air from a system loaded with highly-viscous matter may be difficult or impossible especially where air bubbles are not initially only near the system""s outlet. This is because air bubbles will simply not be able to buoy to a point where they may be ejected without extruding a large volume of the implant material intended for implantation from the applicator.
Specific adaptation for venting or purging of air from a syringe for delivering viscous material is disclosed in U.S. Pat. No. 4,795,444 to Hasegawa et al. In this device, space is provided in a top section of the syringe so that an end of a plunger may pass through material in the top section to vent air bubbles before forming a seal in the smaller diameter bottom section of the syringe. The differential in sizes of the sections may be provided in stepwise fashion, as a tapered wall or as by a recessed channel. All this being said, as stated previouslyxe2x80x94a syringe is of limited utility or practicality as a high pressure applicator and cannot be effectively used as an applicator in the present invention due to various shortcomings inherent to the limitations of syringes as discussed above.
Accordingly, especially for use with PMMA in percutaneous vertebroplasty procedures, there exists a need for an improved system able to provide substantially non-complaint and precise application of implant material under high pressures to a desired location in a single batch. The system of the present invention includes method and apparatus adapted to meet such needs as well as provide other advantages readily apparent to those with skill in the art.
The present invention is an improved system for controlled delivery of injectable material to a patient. It includes a first column including a vessel section open to an implant material introduction section. A second column is provided which is drivably engageable with the first column along an advancement axis. Handles may be provided on the first and second columns for manual actuation of the device by turning the columns relative to each other where a threaded interface is provided. A piston or plunger member is provided and advances within the vessel section of the first column upon advancement of the second column to generate pressure to drive implant material loaded within the vessel section. Although a close-tolerance or slight interference fit between the piston and the vessel section may be provided to develop a seal, it is preferable to provide an O-ring or other sealing element as typically done in the art.
The introduction section of the first column has a slightly larger cross-sectional area than that of the portion of the vessel section adjacent to it. Providing a larger size or diameter introduction section than vessel section entrance enables the introduction of the piston into the implant material without simultaneously forming a seal where compliant bubbles may be trapped. Put another way, the differential in sizes is provided so that when the vessel section is fully filled and the introduction section is at least partially filled, the end of the piston may be dipped in the implant material to allow for the exclusion of air bubbles prior to driving it into the vessel section.
Where the implant material is less viscous, the piston may merely be plunged in to implant material in the introduction section and driven into the vessel section. Where the implant material is more viscous, it may be advisable to more carefully place the piston in contact with the implant material in the introduction section to avoid air bubbles (by turning, rocking or otherwise manipulating the piston) and then inserting it into the vessel section where a seal is formed.
The introduction section of applicator in the present invention may be relatively close in size to the vessel section entrance to provide only a surrounding dam for a meniscus poured over the vessel section. Since the amount of material to be provided in the introduction section need not be great to facilitate the venting or purging as described above, in using the invention it is better to only introduce slightly more implant material than will fill the vessel. Introduction of a larger amount of implant material is not only wasteful, but may result in material drainage out of the introduction section into other parts of the applicatorxe2x80x94especially when the applicator is inverted or turned as will often be the case in preparing PMMA implant material for delivery.
To help account for the possibility of excess implant material and associated potential of fouling of the applicator by such excess, a larger size of the introduction section than strictly required for the venting feature discussed above may be used to act as a catch basin for implant material. This will provide an increased margin of error in pouring implant material into the applicator before overflowing the introduction section. Further, the walls of such an enlarged catch basin may help to prevent contamination of the applicator by virtue of adherence of the implant material to the surface area provided during inversion or agitation of the applicator.
The present invention may include a funnel or increased-size target region integrated into the first column, adjacent to the introduction section, to aid in pouring implant material into the applicator. Drive threads may be placed on the exterior of the funnel section. However, when no integral funnel is provided, drive threads may be placed exterior to the introduction section which may be of a finer pitch or higher thread count than those on a larger diameter. A smaller diameter and/or finer threads will provide for greater mechanical advantage for generating higher driving pressures more easily. To help in loading material into the applicator when no integral funnel is used, a separate funnel element may be provided to interface with the introduction section.
The present invention includes such features of the pressure applicator discussed above as well as the methods involved in preparing and using the applicator to inject material into a patient. Such methods or procedures involve preparing an applicator by at least partially filling an introduction section with a material for delivery above a level at which a piston may form a seal and driving a piston head into a vessel section bore where a seal is formed without the introduction of compliant matter such as air bubbles. The preparation method may be followed by introducing material from the applicator into a patient in a medical procedure that may be distinct and separate from the inventive preparation method.
The invention also includes those concomitant parts or elements useable with the applicator in delivering material to a site within a patient. Such elements may include a delivery hose, a cannula (alone or in combination with one or more stylets) and vertebroplasty implant material. Reference is made to preferred embodiments of these elements which are described in further detail below. Together, these elements may form part of the inventive kit or system to be used in a procedure or method as variously described herein.